More adults are obese than underweight worldwide — and one in five could be obese by 2025, a new study found.

Obesity in men has tripled and more than doubled in women, according to the research by scientists from Imperial College London who compared the body mass index (BMI) among almost 20 million men and women from 1975 to 2014.

More than one-quarter of severely obese men and nearly one-fifth of severely obese women live in the US, the researchers said. The US has 41.7 million obese men and 46.1 million obese women.

Professor Majid Ezzati, lead author of the study published in The Lancet medical journal, called it an “epidemic of severe obesity.”

The study pooled data from adults in 186 countries and found that the number of obese people had shot up from 105 million in 1975 to 641 million in 2014.

Meanwhile, the number of those underweight had climbed from 330 million to 462 million in the same period.

The proportion of underweight people fell from 14 percent to 9 percent of men and from 15 percent to 10 percent of women, according to the study.

Global obesity rates among men went up from 3.2 percent in 1975 to 10.8 percent, while among women they rose from 6.4 percent in 1975 to 14.9 percent.

This equates to 266 million obese men and 375 million obese women in the world in 2014.

People are divided into healthy or unhealthy weight categories based on their BMI — a ratio of weight-to-height squared. A healthy BMI ranges from 18.5 to 24.9.

“Our research has shown that over 40 years we have transitioned from a world in which underweight prevalence was more than double that of obesity, to one in which more people are obese than underweight,” Ezzati said, the BBC reported.

“Although it is reassuring that the number of underweight individuals has decreased over the last four decades, global obesity has reached crisis point.”

He said he hoped the findings will spur governments to develop and implement policies to address obesity.

“For instance, unless we make healthy food options like fresh fruits and vegetables affordable for everyone and increase the price of unhealthy processed foods, the situation is unlikely to change,” he said.

The probability of reaching the World Health Organization’s global obesity target — which aims for no rise in obesity above 2010 levels by 2025 — would be “close to zero,” the BBC reported, citing the study.

The research also found that almost a fifth of the world’s obese adults — 118 million — live in only six high-income English-speaking countries: the US, Australia, Canada, Republic of Ireland, New Zealand and the UK.

“There will be health consequences of magnitudes that we do not know,” Ezzati told AFP.

“Obesity and especially severe and morbid obesity, affect many organs and physiological processes,” he said. “We can deal with some of these, like higher cholesterol or blood pressure, through medicines. But for many others, including diabetes, we don’t have effective treatment.”